Fluid ejection devices such as printer ink cartridges use resistors formed on an integrated circuit to vaporize fluid held in a chamber, ejecting a droplet of fluid through a nozzle. For various reasons it can be beneficial to preheat the fluid prior to vaporization. Trickle warming is an exemplary pre-heating technique. Prior to ejecting fluid, a first transistor formed on the integrated circuit switches a “trickle” current. The current causes the resistor or the first warming transistor to pre-heat but not vaporize fluid in a chamber. Subsequently, a second firing transistor formed on the integrated circuit switches a firing current to the resistor. The firing current causes the resistive element to vaporize the fluid. The use of two transistors, however, can consume significant area on the integrated circuit that could otherwise be used for any number of other purposes. Moreover, trickle warming can prove to be inefficient in that a substantial portion of the energy used to heat the ink is dissipated in the integrated circuit instead of the ink.